Thermo-economic performance enhancement in batch evaporation process via mechanical vapor recompression system coupled with steam accumulator

Abstract

Energy consumption in batch evaporation process has aroused widespread concern around the world. In this investigation, a mechanical vapor recompression system coupled with steam accumulator (MVR-SA) was proposed to reduce the start-up time and enhance energy efficiency during the batch evaporation process. Mathematical models were established considering the first and second laws of thermodynamics and relevant economic theory. Performance analysis was carried out from energy, exergy and economic viewpoints. Experimental results showed that the MVR-SA system could achieve distinctly faster intermittent start-up than conventional MVR. Energy efficiency ratio was experimentally obtained as 6.25, the input exergy, output exergy, exergy destruction and exergy efficiency were 21.7 kW, 2.04 kW, 19.66 kW and 9.4%, respectively. Simulated results indicated that increasing the heat transfer temperature difference of heat exchanger and liquid level height of steam accumulator, or decreasing evaporation pressure, could increase the system input exergy and exergy destruction, which reduced the system exergy efficiency. The optimum compression ratio and heat transfer temperature difference were obtained to achieve the minimum total cost considering annual investment, operation and environmental costs. Finally, an economic performance comparison confirmed greater superiority for the novel MVR-SA compared to conventional single effect system in the batch evaporation fields.